1. Field of the Invention
The present invention relates to apparatus and a method for converting light signals into electrical signals. More particularly, it is related to a semiconductor photodetector device especially suitable for converting high frequency electromagnetic radiation signals, particularly long wavelength infrared signals, into electrical signals using a quantum well.
2. Background Information
In known photodetectors, the photons excite electrons in the valence band of the semiconductor material causing them to jump from the valence band to the conduction band. Such devices are termed "interband" photodetectors as electrons are excited from one band, the valence band, to a second band the conduction band. Such prior art devices are useful at short wavelengths.
One application of such prior art photodetectors is as a receiver in digital communications systems using fiber optic channels. In the systems, digital data, and or, voice or video data converted to digital signals, generate light pluses which are transmitted over the fiber optic channels. Typically, such light is produced by a laser in the infrared range. As improvements in optical fiber technology have occurred, it has become possible to increase the number of light pluses per second that may be transmitted to where it is now possible to transmit pulsed light signals at rates in excess of one gigahertz (GHz) with a strong trend toward higher rates. Due to losses in the fiber optics at short wavelengths in the near infrared region, it is necessary in such systems to provide repeaters which adds to the cost and complexity of the system.
Advances in fiber optic technology are leading to the development of long wavelength, low loss optical fibers which are much more suitable for long distance communication. Unfortunately, the "interband" photodetectors which are useful at short wavelengths are less suitable for long wavelength data communication.
There exists, therefore, a real need for fast response, long wavelength photodetector which is capable of rapidly converting light signals into electrical signals.
It is therefore a primary object of the invention to provide an apparatus and method capable of converting long wavelength light signals into electrical signals.
It is another important object of the invention to provide an apparatus and method capable of converting long wavelength light into electrical signals at high pulse rates with minimal error.